Motor control device

ABSTRACT

The present invention relates to a motor control device using an inverter or inverters, in particular, it relates to a motor control device suitable for the prevention of inertial rotation of a motor or motors or for the maintenance of synchronized operation of a plurality of motors in a service-interruption time; a DC side voltage is compared with a target voltage and a correction signal relating to the deviation voltage is added to a speed instruction for the inverter; thereby in a service-interruption time a motor can be continuously and smoothly decelerated keeping the DC side voltage of an inverter at a target voltage value. By utilizing a motor control device according to the present invention for a spinning machine etc., unevenness in thread winding or thread cut in a service interruption time can be prevented.

TECHNICAL FIELD

The present invention relates to a motor control device using aninverter or inverters, in particular, it relates to a motor controldevice which is suitable for the prevention of inertial rotation at aservice interruption, or for the maintenance of synchronized operationof a plurality of motors.

BACKGROUND ART

In spinning machinery such as a spinning machine, the driving rotationalspeed of spindle and the driving rotational speed of other peripheralequipment must have fixed synchronous relation with each other.

Recently, with the increasing demand for energy saving or for givingflexible production functions, the use of ring spinning machines of adirect driving system has increased in which system, for each spindle, amotor is provided separately from that for driving peripheral equipment,and the motors are controlled to be driving at a variable speed.

In a spinning machine of a direct driving system, the above-mentionedfixed rotational synchronization is given by the rotational speedcontrol of the motors for the spindles and the peripheral equipment.

In the case of a spinning machine etc. of a direct driving system, whilea motor for driving a spindle and a motor for driving other peripheralequipment are operated by a power supply, a fixed synchronous relationin rotational speed is maintained, but if the supply of electricity fromthe power supply is interrupted by a trouble etc., that is, in a serviceinterruption, the operation of an inverter cannot be continued andmotors are rotated by inertia making the speed control impossible;therefore, during a period of time, from a normal operating conditiontill each of the parts being driven comes to a stop, the above-mentionedsynchronous relation can be broken. As a result, there is a probabilitythat a defect is produced in a product or thread cut occurs.

An idea to continue the speed control of a motor even in the case of aservice interruption by continuing the operation of an inverterutilizing the regenerative power from the motor is shown in a Japanesepatent, laid open No. 62393/86. In the disclosed idea, the followingoperation is performed: in a service interruption, an instruction torapidly lower the output frequency of an inverter is issued; when thevoltage on the DC side of the inverter is made to an overvoltage withthe feedback of the regenerative power, the instruction is suspended tostop the feedback of the regenerative power; when the voltage on the DCside of the inverter is lowered by the stop of the feedback theinstruction is issued again, and the feedback operation of regenerativepower is performed; such an operation is repeated until the motor isdecelerated to a certain speed. Therefore, every time when aninstruction is issued, deceleration is performed at the samedeceleration rate and the instruction is suspended when the voltage onthe DC side of the inverter is made to an overvoltage by regeneration;thus rapid deceleration of the motor and the stop of deceleration isrepeated (ON/OFF control), so that a problem results in this case isthat smooth deceleration of the motor cannot be performed. Because ofthis, when the technique is applied to spinning machinery such asspinning machines, there occurs a problem of thread cut or unevenness inthread winding caused by off and on speed change. Since the decelerationrate is set to be large, the quantity of regeneration becomes large, sothat the voltage on the DC side rises so high as to induceover-excitation, and a lot of regenerative energy is consumed in themotor, which shortens the period of time in which the voltage of the DCside can be maintained, and a problem occurs that if the duration oftime of a service interruption becomes long, restarting of the motorbecomes difficult.

SUMMARY OF THE INVENTION

An object of the invention is to provide a motor control device which iscapable of controlling the rotation of a motor to be deceleratedcontinuously and smoothly even when a service interruption occurs.

A motor control device according to the present invention comprises: aninverter whose DC side is connected to a power supply, and the AC sidethereof is connected to at least a unit of a motor; a speed settingmeans for giving a speed instruction to the inverter; aservice-interruption detection means for detecting a serviceinterruption of the above-mentioned power supply; a voltage detectionmeans for detecting a DC-side voltage of the inverter; a target-voltagegeneration means for generating a target voltage; a comparison means forcomparing the voltage detected by the voltage detection means and thetarget voltage and for outputting the deviation voltage; and a speedcorrection means for generating a speed correction signal which iscontinuously changed in connection with the output of the comparisonmeans; and a DC-side voltage of the inverter is kept at a target voltagevalue by adding with an adder the output of the speed correction meansto the output of the speed setting means for continuously changing theoutput of the speed setting means, on the direction of a serviceinterruption by the service-interruption detection means. In the motorcontrol device according to the present invention a motor and aninverter are connected even in a service interruption, and the voltageof the DC circuit of the inverter is maintained at a proper value andthe control is continued by the regenerative power; therefore theinertial operation of the motor is prevented and the speed is correctedby the speed correction means corresponding to the deviation voltagebetween the target voltage and the detected voltage, so that therotation of the motor can be continuously and smoothly decelerated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a basic constitution of the presentinvention;

FIG. 2 is a time chart showing a DC circuit voltage and a speedinstruction in a service interruption according to the presentinvention;

FIG. 3 shows waveform diagrams of a voltage and a frequency in a serviceinterruption according to the present invention;

FIG. 4 shows time charts of a DC circuit voltage and the rotationalspeed of a motor in a service interruption in an embodiment of thepresent invention;

FIG. 5 shows time charts of a DC circuit voltage and the rotationalspeed of a motor in a service interruption according to the presentinvention;

FIG. 6 is a block diagram showing a concrete constitution of a firstembodiment of the present invention;

FIG. 7 shows time charts of a DC circuit voltage and the rotationalspeed of a motor in the case where a braking effect is improved in aservice interruption in the present invention;

FIG. 8 is a block diagram showing the constitution of a secondembodiment of the present invention;

FIG. 9 is a block diagram showing the constitution of a third embodimentof the present invention;

FIG. 10 shows time charts of a DC circuit voltage and the rotationalspeed of each of the motors in the present embodiment;

FIG. 11 is a block diagram showing the basic constitution of a fourthembodiment of the present invention;

FIG. 12 is a block diagram showing the basic constitution of a fifthembodiment of the present invention; and

FIG. 13 is a block diagram showing the basic constitution of a sixthembodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention and the embodiments will be explained referring toFIG. 1 to FIG. 13.

The basic constitution of the present invention will be explainedreferring to FIG. 1 to FIG. 5.

FIG. 1 shows the basic constitution of the present invention. The DCside of an inverter 103 is connected to a power supply 101 and a motor105 is connected to the AC side of it. A service-interruption detectionmeans 116 for detecting a service interruption is connection to thepower supply 101. A voltage detection means 110 for detecting thevoltage on the DC side (hereinafter referred to as DC circuit) of theinverter 103 is connected to the DC side of the inverter 103. To thevoltage detection means 110, a comparison means 140 is connected whichcompares the voltage detected by the voltage detection means 110 with atarget voltage produced by a target voltage generation means 112 forgenerating a target voltage for the DC circuit, and outputs thedeviation voltage. The output of the comparison means 140 is connectedto a speed correction means 111 provided with a switch means S which isactivated when a service interruption is detected by theservice-interruption detection means 116. The output of the speedcorrection means 111 is connected to an adding means 142 which isconnected between a speed setting means 107 and the inverter 103.

The operation in the constitution as shown in FIG. 1 will be explainedreferring to FIG. 2 to FIG. 5.

The voltage detection means 110 detects the DC circuit voltage of theinverter 103; the comparison means 140 compares the output of thevoltage detection means 110 with a target voltage E generated by thetarget voltage generation means 112, and outputs the deviation voltage.The speed correction means 111 outputs a speed correction signal whichvaries continuously in connection with the deviation voltage. The speedcorrection signal is arranged to be generated when a serviceinterruption is detected by the service-interruption detection means116. In other words, in the speed correction means, a switch S isprovided which performs ON/OFF operation according to the signal of theservice-interruption detection means 116. The switch S can be the one asdescribed in the following: the switch S is provided between the outputof the comparison means 140 and the input of the speed correction means111, and it is made ON by the output of the service-interruptiondetection means 116 in the case of a service interruption to supply theoutput of the comparison means 140 to the speed correction means 111; itis also provided for short-circuiting the input and the output of thespeed correction means 111 in normal time, and in a service interruptionit is made OFF to make the speed correction means 111 workable. In thecase of the occurrence of a service interruption, with the ON or OFF ofthe switch S, the speed correction means is made to be capable ofoutputting a speed correction signal. The speed setting means 107generates an output to rotate the motor 105 at a specified speed. In aservice interruption, the output of the speed correction means 111 isadded to the output of the speed setting means 107 through the addingmeans 142; thereby, the output of the speed setting means 107 iscontinuously corrected and the speed instruction is continuouslydecreased, and the motor 105 is continuously decelerated following theinstruction.

The states of the voltages and the speed after the occurrence of aservice interruption will be explained referring to FIG. 2 and FIG. 3.As shown in FIG. 2, wherein a service interruption occurs, the output ofthe service-interruption detection means 116 falls stepwise, and thetrailing edge is output as a low level service-interruption signal (FIG.2(a)). The switch S is activated by the signal, and the speed correctionmeans 111 generates an output in connection with the above-mentioneddeviation voltage.

On the other hand, as shown in FIG. 2, the DC voltage VDC starts to fallsimultaneously with the time of occurrence of a service interruption t0,and the detected voltage by the voltage detection means 110 becomeslower than the target voltage E given by the target voltage settingmeans 112 (FIG. 2(c), t0 to t2), so that the deviation voltage betweenthe detected voltage and the target voltage becomes a negative value,and the voltage is input to the speed correction means 111.

The operation after the occurrence of a service interruption ismaintained by supplying the regenerated power through the inverter 103to each constituent element by way of the control power supply 117(omitted in FIG. 1). Detailed description will be given below. When thedeviation voltage is input to the speed correction means 111, it outputsa specified speed correction value obtained by integrating the deviationvoltage (FIG. 2(d)); the value is added to the speed instruction fromthe speed setting means 107; therefore, if a negative deviation is inputas mentioned in the above, a correction value corresponding to thedeviation voltage is subtracted from the speed instruction given by thespeed setting means 107, and the speed instruction for the inverter 103decreases (FIG. 2(e)).

In an early stage of a service interruption, the number of revolutionsof the motor 105 is kept almost as it was by an inertial force, so thatthe inverter 103 starts regenerative operation after t1 sec from themoment of occurrence of a service interruption caused by the decrease ofspeed instruction as mentioned in the above, and after t2 sec from theoccurrence of the service interruption a state is obtained where the DCvoltage E is generated (FIG. 2(c), t2 to t5) by the regenerative powerfrom the motor 105. During such a period of time, the motor isdecelerated keeping the DC voltage E, and when the speed is lowered tilla certain value, it becomes impossible to generate regenerative powerand reaches a stop (FIG. 2(e), t0). The voltage, the speed and the flowof energy during the decelerating operation in t3 to t4 will beexplained referring to FIG. 3.

In the present embodiment, since the comparison means 140 and the speedcorrection means 111 function as a feedback system, as shown in FIG.3(a), they operate as a feedback control system to make the DC voltageVDC converge at the target voltage E.

In other words as shown in FIG. 2(b), when the deceleration of the motor105 grows larger than the speed instruction, the regenerative powerfalls short of keeping the DC voltage VDC and the VDC is lowered much tobe lower than the target voltage E, so that the decreasing speed of thespeed instruction is decelerated by the decrease in correction value; onthe other hand when the deceleration of the motor 105 is slower than thespeed instruction the regenerative power becomes surplus, and the DCvoltage VDC rises much to be higher than the target voltage E, so thatthe correction value increases and the decreasing speed of the speedinstruction is accelerated. Thereby, the energy flow between theinverter and the motor becomes as shown in FIG. 2(c). Thus the feedbackcontrol is executed in the form in which the DC voltage VDC is made toconverge at the target voltage E by the increases or the decrease of thecorrection value, and the motor 105, keeping the DC voltage E, isgradually decelerated with the decrease of rotating energy beingconsumed in the heating of windings, etc. in the flow of energy as shownin the above. When the speed is lowered much, the quantity ofregenerative energy is decreased and the DC voltage begins to fallwithout being able to maintain the target value. Owing to this, thedeviation voltage between the DC voltage and the target value becomeslarge, and the correction quantity for the speed instruction isincreased and the deceleration for the motor is expedited to bring it toa stop.

As described in the above, in the present embodiment a correction signalis obtained by integrating the deviation voltage, so that the correctionquantity can be made large by the accumulation of the deviation voltage,that is, the voltage fluctuation can be decreased and the speedstabilization can be achieved. After the occurrence of a serviceinterruption, a shown in FIG. 4, the DC voltage VDC can be kept at thelevel of the target voltage E for a long time; owing to this even afterthe occurrence of a service interruption the control of the inverter 103can be continuously performed; thereby the motor 105 can be deceleratedcontinuously and smoothly while being controlled by the inverter 103.

As described in the above, after the occurrence of a serviceinterruption, energy is regenerated by the motor 105, and the DC voltageVDC is kept at the level of the target voltage E for a long time by afeedback control; thereby the control of the inverter 103 iscontinuously performed and the electrical relation between the motor 105and the inverter 103 is maintained; therefore, in the case of a serviceinterruption, after the service is recovered the resumption of operationis easy. After the recovery of the service, the generation of thecorrection signal by the speed correction means is stopped, so that themotor is accelerated smoothly at a specified rate as shown in FIG. 5.

A first embodiment of the present invention will be explained referringto FIG. 6.

In the present embodiment, the invention is applied to a motor controldevice to be connected to an AC circuit.

In the present embodiment, a power supply 501 is the AC commercial powersupply.

The present invention comprises the following, an addition to theconstitution shown in FIG. 1: a converter 502 connected between theinverter 103 and the power supply 501, a smoothing capacitor C connectedto the DC circuit of the inverter 103, and an oscillator 508 and a PWMconverter 509 being connected in series which are connected between aspeed setting means 107 and an adding means 142.

In a voltage detector 116 in the present embodiment, resistors R 509 andR 510 connected in series to each other are connected to the powersupply 501 through a rectifier D 501. The junction point of resistors R509 and R 510 is connected to one of the inputs of a comparator Q 503,and the other input of the comparator Q 503 is connected to a resistor R511 which generates a criterion voltage whose another end is connectedto the positive side of a control power supply 117.

The comparator Q 503 compares a voltage between both ends of theresistor 510 (a divided voltage value of the recited power supplyvoltage) and the criterion voltage set by the resistor R 511, anddetects a service interruption by detecting the voltage between bothends of the resistor R 510 to be lower than the criterion voltage set bythe resistor R 511, and generates a signal. In the present embodiment,the comparator Q 503 generates a high level signal in the normal voltagetime, and in the lower voltage time, such as a service-interruptiontime, it generates a low level signal as a service-interruptiondetection signal.

A voltage detector 110 is composed of resistors R 501 and R 502connected in series to each other, and the output is taken out from theresistor 502.

A target voltage generating means 112 comprises a resistor R 503 whoseone end is grounded and the other end is connected to the negative sideof the control power supply 117, and the target voltage is obtained bydividing the voltage applied to the R 503.

The comparison means 140 comprises: an amplifier Q 501; a resistor R 504connected to the input terminal of the amplifier Q 501 and to thevoltage detector 110; and a resistor R 505 connected to the inputterminal of the amplifier Q 501 and to the target voltage generationmeans 112. The amplifier Q 501 further comprises a negative feedbackresistor R 506 between the input terminal and the output terminal. Theoutput of the voltage detector 110 and the output of the target voltagegeneration means 112 are superimposed at the junction point of resistorsR 504 and R 505, and the deviation voltage between them is input to theamplifier Q 501 and amplified to be output to the speed corrector 111.

In the present embodiment, the speed corrector 111 comprises anamplifier Q 502, and a resistor R 507, as a proportional element, and acapacitor C 501, as a differential element, being connected in parallelto each other are connected between the output terminal of thecomparison means 140 and the input terminal of the amplifier Q 502. Aresistor R 508 and a capacitor C 502 connected in series to each otherare connected between the input terminal and the output terminal of theamplifier Q 502 as a proportional integration element, and further aswitch S is connected in parallel to the proportional integrationelement. The switch S is normally made ON by the output of thecomparator Q 503 in the service-interruption detection circuit 116, andwhen the voltage is lowered as in the case of a service interruption, itis made OFF.

In the present embodiment, in the normal operation, DC power having a DCvoltage E is supplied to the inverter 103 from the commercial powersupply 501 through the converter 502. At this time, the inverter 103drives the motor 105 in a number of revolution corresponding to a speedinstruction issued from the speed setter 107. In this case, theinstruction from the speed setter 107 is changed to a ramp-shaped signalin a mild acceleration/deceleration circuit 533, and the magnitude ofthe signal at each point of time in the ramp part is proportional to anoutput frequency. A specified frequency signal is input to the PWMconverter 509 from the oscillator 508 by the above-mentioned signal, andfrom the PWM converter 509 a PWM signal is generated which makes theinverter 103 output an AC power having a voltage V1 and a frequency F1corresponding to the ramp signal (speed instruction); by the PWM signal,the inverter 103 is operated and the motor 105 is driven in a number ofrevolution corresponding to a speed instruction.

In this embodiment, since a PWM system inverter is used, there is noneed to control DC voltage VDC; therefore, the voltage VDC is kept at analmost constant voltage which is obtained by simply converting (fullwave rectification) an AC voltage received from the commercial powersupply 501.

When a service interruption occurs, the DC voltage VDC begins to fall,and the deviation voltage between a detected voltage by the voltagedetector 110 and the target voltage becomes a negative value, and it isinput to the speed corrector 111.

When the deviation voltage is input to the speed corrector 111, thecorrector works to output a specified speed correction value obtained inprocessing the deviation voltage by proportion, integration ordifferentiation. The output is added to the speed instruction from thespeed setter 107 in the adder 142; when a negative deviation voltage isinput, a correction quantity corresponding to the deviation voltage issubtracted from the speed instruction given by the speed setter 507, andthe speed instruction for the oscillator 508 is decreased. Owing tothis, the motor 105 is made to be in a regenerative condition, and thespeed instruction is corrected in relation to the deviation voltagebetween the voltage of the DC circuit and the target voltage, so that,similar to the case of basic constitution, the motor 105 is deceleratedcontinuously and smoothly in the state where the voltage of the DCcircuit is kept at the target voltage value E. The operations after theoccurrence of a service interruption are sustained by the control powersupply 117 connected to the DC circuit.

In the present embodiment, it is possible to adopt a constitution inwhich the setting of a target voltage is performed by a microcomputer(CPU). In other words, it is possible to have a constitution in whichthe functions to be performed by the voltage detector 110, the targetvoltage setter 112, the mild acceleration/deceleration circuit 533, theadder 142, the oscillator 508, and the PWM converter 509 are executed bythe microcomputer (CPU).

In the above constitution, during a deceleration process in a serviceinterrupt in, the microcomputer monitors the speed of the motor 105 (orspeed instruction) and when the speed falls to a certain low sped regionit resets the target voltage of the DC circuit to a hither value asshown in FIG. 7. Thereupon, the deviation voltage from the detectedvalue is suddenly increased, so that the microcomputer makes the speeddeceleration quantity larger. In other words, it controls to deceleratethe motor at a larger rate to make the feedback quantity of theregenerative energy large and to push the DC voltage up to a new targetvoltage level as shown in FIG. 7(b). At this time, the energy increasedby square times of a voltage ratio is accumulated in the capacitor C,and the speed of the motor 105 falls to a very low level because of asudden deceleration as shown in FIG. 7(c). At this time, themicrocomputer CPU applies dynamic brakes (DC brake) to the motor throughthe inverter utilizing increased energy in the capacitor C. Thereby, themotor 105 is securely stopped.

A second embodiment according to the present invention will be explainedreferring to FIG. 8. In FIG. 8, similar symbols are given to similarconstituent elements to those in the firsts embodiment. In the presentembodiment, the DC circuits of an "A" system and a "B" system havingseparate main circuits and control circuits to be able to operate eachsystem independently from each other are connected to each other to forma common DC circuit, and the regenerative energy of a system havinglarger inertial energy is arranged to be supplied to the other system.

In the present invention, a system which has large inertial energy of aload and a motor and whose energy which can be regenerated for theduration of a service interruption is larger than the consumption energyfor continuing the operation of a "B" system is selected to be an "A"system, and the "A" system has similar constitution to that of the firstembodiment.

The "B" system has a power supply 501 in common with the "A" system, andcomprises a converter 502B connected to the power supply 501, and aninverter 103B having a DC circuit connected to the converter 502B. Amotor 205 is connected to the AC side of the inverter 103B, and asmoothing capacitor C is connected to the DC side of the inverter 103B.The control circuit of the inverter 103B comprises: a speed setter 107B,a mild acceleration/deceleration circuit 533B connected in series to theoutput of the speed setter 107B, an oscillator 508B, and a PWM converter509B; the output of the PWM converter 509B is connected to the inverter103B.

In the present embodiment, the DC circuit of the inverter 103 in the "A"system and the DC circuit of the inverter 103B of the "B" system areconnected to each other to form a common DC circuit.

Owing to this arrangement, the "A" system can feedback regeneratedenergy to the common DC circuit when a power supply is interrupted.

When a service interruption occurs in the "A" system, similar to thefirst embodiment, a negative feedback control is executed to make thevoltage of the common DC circuit converge at a target voltage, andcontinuous and smooth deceleration of the motor is performed. On theother hand, the "B" system independently comprises: a speed settingcircuit 507B, the mild acceleration/deceleration control circuit 533B,the oscillator circuit 508B, and the PWM converter circuit 509B;therefore, the "B" system is operated independently in a different wayfrom the "A" system. That is, when the operation is continued in a motorregion, the energy fed back from the "A" system can be utilized for thecontinuation of the operation of the "B" system.

When the regenerative energy of the "A" system is large, a plurality of"B" systems can be connected to the "A" system in the range where theenergy of the "A" system can afford to support "B" systems. In place ofthe converters 502 and 502B of the "A" system and the "B" system acommon converter can be used.

A third embodiment according to the present invention will be explainedreferring to FIG. 9. In the present embodiment, an "A" system comprisesa speed ratio circuit 513 connected between an adder 142 and anoscillator 508, and an oscillator 508B and a PWM converter circuit 509Bof a "B" system are connected to the speed ratio circuit 513.

The constitution of the "A" system is similar to that of the secondembodiment except that the speed ratio circuit 513 is connected betweenthe adder 142 and the oscillator 508. The constitution of the "B" systemis similar to that of the second embodiment except that the oscillatorcircuit 508B and the PWM converter circuit 509B are connected to thespeed ratio circuit 513 of the "A" system. In the present embodiment,the speed ratio circuit 513 devices the speed ratio of a motor MB 205 inthe "B" system to a motor MA 105 in the "A" system, and the motor MB 205and the motor MA 105 are operated at a specified speed ratio(synchronized operation).

In the present embodiment, in the case of a power interruption, thefeedback of regenerative energy can be done by either of the systems,and the feedback quantity of regenerative energy, that is, thedeceleration rate of motors MA and MB in both systems A and B, isautomatically controlled to make the voltage of the common DC circuit,regarding A and B systems as a single system, converge at a targetvoltage value. The operations of motors MA and MB in both systems arecontinued keeping a specified speed ratio by the speed ratio circuit513.

In FIG. 10, the relation between the DC voltage VDC and the sped ofmotors MA and MB during the period of time of continuation ofsynchronized operation in a service operation. After the occurrence of aservice interruption, the motors in both systems are smoothlydecelerated in synchronization with each other keeping the VDC of thecommon DC circuit at a target value. The synchronized operation isnormally performed till a low speed state.

A fourth embodiment according to the present invention will be explainedreferring to FIG. 11. The present embodiment is an example in which thepresent invention is applied to a motor control device for a ringspinning machine. In the present embodiment, a motor 105 is a spindlemotor, and a motor 205 is the one to be used for a peripheral mechanismportion such as a draft mechanism portion. The spindle motor 105 and themotor 205 for the peripheral mechanism are directly connected to aspindle and to a peripheral mechanism as a direct driving system, andaccording to the scale of a spinning machine, they are provided one unitor a plurality of units respectively. Inverters 103 and 103B arerespectively connected to a unit of spindle motor 105 or a plurality ofspindle motors 105 and to a unit of motor 205 or a plurality of motors205 for peripheral mechanism.

In the present embodiment, the constitution is similar to that of thethird embodiment except that a converter 502 is commonly provided forinverters 103 and 103B, and a speed ratio circuit 113 is connectedbetween the oscillator circuit 508B of the inverter 103B and the adder142. In FIG. 3, a smoothing capacitor C of the DC circuit is omitted.

In the present embodiment too, the voltage of the DC circuits of theinverters 103 and 103B are detected and a feedback control is executedso that the voltage can be kept at a target voltage value even in aservice interruption, and the speed instruction is correctedcorresponding to the deviation voltage between the detected voltage andthe target voltage.

In the present embodiment, a signal of a specified frequency is input toa PWM converter 509 from an oscillator 508 according to a speedinstruction output form a speed setter 107, and from the PWM converter509 a PWM signal is generated which makes the inverter 103 output an ACpower having a voltage V1 and a frequency f1 corresponding to the speedinstruction. Owing to this, the motor 105 is driven in a number ofrevolution corresponding to the speed instruction.

The speed instruction is supplied also to an oscillator 508B and to aPWM converter 509B through the speed ratio setter 113, and from the PWMconverter 509B a PWM signal is output to make the inverter 103B outputan AC power having a voltage V2 and a frequency f2 to make the ratio ofthe number of revolution of the motor 205 to the number of revolution ofthe motor 105 be a specified value; owing to this, the motor 205 isdriving in a number of revolution of a speed ratio given by the speedratio setter 113 for the speed instruction at the time. In the presentembodiment, control is so executed that a specified relation between aninstruction and an output can be realized in both voltage and frequency,that is, f1/f2=a constant, and V1/V2=a constant, and the motor 105 andthe motor 205 are operated in synchronization with each other.

Because of this, even if the quantity of inertial energy GD maintainedby the whole take-up mechanism including the spindle motor 105 ischanged by the quantity of thread taken up by a spindle, beingindependent of the change, a control is automatically obtained whichmakes motors stop always keeping a proper speed ratio.

When power supply is recovered during a decelerating operation, that is,at the so called recovery of a service interruption, the recovery isdetected by a service-interruption detector 116, and the output of thespeed corrector 111 is made to zero by the operation of a switch S.Thereupon, the speed instruction returns to a value before the serviceinterruption; in the result, motors 105 and 205 are accelerated again tobe brought back to the number of revolution in the normal operatingcondition.

In the case of the re-acceleration, if a speed instruction risesstepwise, a too heavy current will flow int he motor and also the speedratio of the motor 105 to the motor 205 will be deviated; therefore itis preferable to change a step-shaped output at a recovery of power to aramp-shaped output by providing a mild acceleration/deceleration circuit533 between the speed corrector 111 and the adder 142.

In the present embodiment, regenerative power is automaticallycontrolled corresponding to the inertial quantity in a spindle drivingsystem of a spinning machine; therefore, when the present embodiment isapplied to a spinning machine of a direct driving system, etc., alwaysan accurate cooperative stop control of rotational speed can beobtained; even in a service interruption, the operation at an accuratespeed ratio is possible and even in the case of a sudden stop of powersupply, the fear for the occurrence of thread cut, etc. can becompletely eliminated; and the lowering of working ratio, the loweringof quality of products and so on can be sufficiently suppressed.

A fifth embodiment according to the present invention will b explainedreferring to FIG. 12.

The present embodiment is an example in which an inverter of PAM systemis used; in the figure 203A and 203B are inverters of PAM system, andthe embodiment is so constituted that each of the motors 105 and 205 aredriven by the above-mentioned inverters respectively.

In the case of an inverter of a PAM system, the control on the AC sidevoltage is executed by controlling a DC input voltage, so that followingthe converter 502, DC choppers 218A and 218B are provided respectively;the DC voltages Ea and Eb are controlled by the above-mentionedarrangement.

Under normal operating conditions: a voltage instruction output from avoltage setter 219 according to a speed instruction from the speedsetter 107 and a detected voltage from the voltage detector 110 arecompared; the deviation voltage is supplied to a chopper driving circuit220A to control the chopper 218A so that the DC voltage Ea can besupplied to the inverter 203A; owing to this, on the AC side of theinverter 203A a voltage V1 corresponding to the speed instruction isobtained. The speed instruction is input also to a frequency setter 221Awhich functions as a first speed control means; thereby the frequency f1on the AC side of an inverter 218A is controlled to be the onecorresponding to the speed instruction. A feedback control means issubstantially composed of a comparator 140 which compares the output ofa voltage detector 110A and the output of a voltage setter 219A, and ofa speed corrector 111 having a switch S.

The inverter 203B and the chopper 218B are controlled by a voltagesetter 219B, a chopper driving circuit 220B and a frequency setter 221Bto be able to supply a specified DC voltage Eb to the inverter 203B andalso to be able to obtain a voltage V2 and a frequency f2 on the AC sideof the inverter 203B; in this case, it is arranged that a speedinstruction is input to the voltage setter 219B and the frequency setter221B through a speed ratio setter 113; because of this the specifiedrelations, f1/f2=a constant, V1/V2=a constant, are given.

Other operations than those mentioned in the above are similar to thosein the fourth embodiment.

Therefore, in this embodiment too, always accurate cooperative stopoperation of a rotational speed is automatically given, and even in thecase of a sudden interruption of power supply caused by a serviceinterruption, the fear of occurrence of thread cut, etc. can be removedcompletely, and the lowering of working ratio of a spinning machine orthe lowering of product quality can be suppressed sufficiently.

A sixth embodiment according the present invention will be explainedreferring to FIG. 13. The present embodiment is a compromise systemcomposed of the combination of the fourth embodiment and the fifthembodiment, in which a spindle driving motor 105 is driven by a PAMsystem inverter 203A, and a peripheral mechanism driving motor 205 isdriven by a PWM system inverter 103. The other constitution than thatmentioned in the above is similar to that of the fourth embodiment or ofthe fifth embodiment, and the operation of each of the constituentelements is also as explained in previous pages. In the presentembodiment: a voltage detector 110 detects a voltage of the DC circuitof the inverter 203A and the voltage is compared with a voltageinstruction value of the voltage setter 219A by a comparator 140 tooutput the deviation voltage; and the output is supplied to a speedcorrector 111, and when the switch S is ON, the output of the speedcorrector 111 is given as a correction signal. The correction signal isadded to a speed instruction of the speed setter 107 to correct thespeed instruction continuously; thereby the inverters 203A and 103 aremade possible to control the speed of motors 105 and 205 continuously.

According to the present invention, regenerative power is automaticallycontrolled corresponding to the inertia quantity in a spindle drivingsystem of a spinning machine; therefore when the invention is applied toa spinning machine of a direct drive system etc.: always an accuratecooperative stop control of rotational speed can be obtained; even in aservice interruption an operation in an accurate speed ratio ispossible; even in a sudden interruption of power supply the fear ofoccurrence of thread cut etc. is completely removed; and the lowering ofworking ratio or the lowering of product quality, etc. can besufficiently suppressed.

What is claimed is:
 1. A motor control device comprising: an inverterwhose DC side being connected to a power supply and to whose AC sidebeing connected at least one motor; a speed setting means for giving aspeed instruction to said inverter; a voltage detection means fordetecting voltages on the DC side of said inverter; a target voltagegeneration means for generating a target voltage on the DC side of saidinverter; a comparison means for comparing a voltage detected by saidvoltage detection means with the target voltage and for outputting adeviation voltage; a speed correction means for generating a speedcorrection signal changing continuously in connection with the output ofsaid comparison means; and an adding means for adding the output of saidspeed correction means to the output of said speed setting means,wherein said speed correction means is provided with a proportionalintegration and differentiation element and generates said speedcorrection signal in connection with a deviation voltage by theproportional integration and differentiation operation and changescontinuously the output of said speed setting means, and said motor isdecelerated continuously keeping the voltage on the DC side of saidinverter at the target voltage in a regenerative operation time of saidmotor.
 2. A motor control device as set forth in claim 1, furthercomprising an oscillation means for supplying a signal having afrequency based on a signal of said speed setting means to the inverter,and a voltage regulation means provided between the DC side of saidinverter and said power supply for supplying a voltage based on thesignal of said speed setting means to said inverter, wherein thefrequency of said oscillation means and the voltage of said voltageregulation means are corrected by a signal of said speed correctionmeans.
 3. A motor control device comprising: an inverter whose DC sidebeing connected to a power supply and to whose AC side being connectedat least one motor; a speed setting means for giving a speed instructionto said inverter; a voltage detection means for detecting voltages onthe DC side of said inverter; a target voltage generation means forgenerating a target voltage on the DC side of said inverter; acomparison mean for comparing a voltage detected by said voltagedetection means with the target voltage and for outputting a deviationvoltage; a speed correction means for generating a speed correctionsignal changing continuously in connection with the output of saidcomparison means; and an adding means for adding the output of saidspeed correction means to the output of said speed setting means,wherein said speed correction means is provided with a proportionalintegration element and generates said speed correction signal inconnection with a deviation by the proportional integration operationand changes continuously the output of said speed setting means, andsaid motor is decelerated continuously keeping the voltage on the DCside of said inverter at the target voltage in a regenerative operationtime of said motor.
 4. A motor control device comprising: a firstinverter whose DC side being connected to a power supply and to whose ACside being connected at least one motor connected to a load with largeinertia of a spinning machine; a second inverter whose DC side beingconnected to the DC side of said first inverter and to whose AC sidebeing connected at least one other motor connected to a load with smallinertia of the spinning machine; a speed setting means for giving aspeed instruction to at least one of said first and second inverters; aservice interruption detection means for detecting a serviceinterruption of said power supply; a voltage detection means fordetecting voltages on the DC side of said first and second inverters; atarget voltage generation means for generating a target voltage on theDC side of said first and second inverters; a comparison means forcomparing a voltage detected by said voltage detection means with thetarget voltage and for outputting a deviation voltage; a speedcorrection means being provided with a proportional integration anddifferentiation element for generating a speed correction signalchanging continuously in connection with the output of said comparisonmeans by the proportional integration and differentiation operation; anda speed ratio decision means for determining the speed ratio betweensaid first inverter and said second inverter, wherein when said serviceinterruption detection means detects a service interruption, the signalof said speed correction means is added to the output of said speedsetting means, and said motors are decelerated keeping the voltage onthe DC side of said first and second inverters at the target voltage andkeeping the speed ratio unchanged in a regenerative operation time ofsaid motors.
 5. A motor control device as set forth in claim 4 furthercomprising a target voltage control means for controlling said targetvoltage generation means, wherein said target voltage control meansraises the target voltage in the case of a large decrease in voltage onthe DC side of said inverter in comparison to desired target voltage,and generates a correction signal to make said speed correction meansincrease the deceleration rate of said motors.
 6. A motor control devicecomprising: a first inverter whose DC side being connected to a powersupply and to whose AC side being connected at least one motor connectedto a load with large inertia of a spinning machine; a second inverterwhose DC side being connected to the DC side of said first inverter andto whose AC side being connected at least one other motor connected to aload with small inertia of the spinning machine; a first speed settingmeans for giving a speed instruction to said first inverter; a secondspeed setting means for giving a speed instruction to said secondinverter; a service interruption detection means for detecting a serviceinterruption of said power supply; a voltages detection means fordetecting voltages on the DC side of said first and second inverters; atarget voltage generation means for generating a target voltage on theDC side of said first and second inverters; a comparison means forcomparing a voltage detected by said voltage detection means with thetarget voltage and for outputting a deviation voltage; and a speedcorrection means being provided with a proportional integration anddifferentiation element for generating a speed correction signalchanging continuously in connection with the output of said comparisonmeans by the proportional integration and differentiation operation;wherein voltages on the DC side of said first and second inverters arekept at the target voltage in a regenerative operation time of saidmotors.
 7. A motor control device comprising: a first inverter whose DCside being connected to a power supply through a voltage regulatingmeans and to whose AC side being connected at least one motor connectedto a load with large inertia of a spinning machine; a second inverterwhose DC side being connected to the same power supply as that of saidfirst inverter and to whose AC side being connected at least one othermotor connected to a load with small inertia of the spinning machine; aspeed setting means for giving a speed instruction to said first andsecond inverters; a service interruption detection means for detecting aservice interruption of said power supply; a voltages detection meansfor detecting voltages on the DC side of said first and secondinverters; a target voltage generation means for generating a targetvoltage on the DC side of said first and second inverters; a comparisonmeans for comparing a voltage detected by said voltage detection meanswith the target voltage and for outputting a deviation voltage; a speedcorrection means being provided with a proportional integration anddifferentiation element for generating a speed correction signalchanging continuously in connection with the output of said comparisonmeans by the proportional integration and differentiation operation,wherein when said service interruption detection means detects a serviceinterruption, the signal of said speed correction means is added to theoutput of said speed setting means, and voltages on the DC side of saidfirst and second inverters are kept at the target voltage in aregenerative operation time of said motors.
 8. A motor control devicecomprising: a first inverter whose DC side being connected to a powersupply and to whose AC side being connected at least one winding motorof a spinning machine; a second inverter whose DC side being connectedto the DC side of said first inverter and to whose AC side beingconnected at least one feeding motor of the spinning machine; a speedsetting means for giving a speed instruction to said first and secondinverters; a service interruption detection means for detecting aservice interruption of said power supply; a voltage detection means fordetecting voltages on the DC side of said first and second inverters; atarget voltage generation means for generating a target voltage on theDC side of said first and second inverters; a comparison means forcomparing a voltage detected by said voltage detection means with thetarget voltage and for outputting a deviation voltage; a speedcorrection means being provided with a proportional integration anddifferentiation element for generating a speed correction signalchanging continuously in connection with the output of said comparisonmeans; and a speed ratio decision means for determining the speed ratiobetween said first inverter and said second inverter, wherein when saidservice interruption detection means detects a service interruption, thesignal of said speed correction means is added to the output of saidspeed setting means, and said winding motor and said feeding motor aredecelerated keeping voltages on the DC side of said first and secondinverters at the target voltage and keeping the speed ratio unchanged.9. A motor control device as set forth in claim 8, wherein said spinningmachine is a ring fine spinning machine, said winding motor is a spindlemotor, and said feeding motor is a peripheral device motor.